The present invention, in some embodiments thereof, relates to polynucleotides encoding BREX system polypeptides and methods of using same.
The ongoing arms race between bacteria and bacteriophages (phages) has led to the rapid evolution of efficient resistance systems to protect bacteria from phage infection (Stern and Sorek, 2011). These systems include restriction-modification systems enzymes that recognize and cleave foreign DNA (King and Murray, 1994), abortive infection (Abi) mechanisms that lead to the suicide of the infected host, thus protecting the colony against phage spread (Chopin et al., 2005), and the CRISPR/Cas adaptive defense system, which uses small RNAs to target and destroy invading phage DNA (Deveau et al., 2010). On the counter arm, as part of this continuous bacteria and phages arms race, successful phages had also developed numerous counter-resistance mechanisms to overcome bacterial defense (Stern and Sorek, 2011). Due to the rapid evolution and elaborated biological novelty associated with the bacteria-phage arms race, it is estimated that many additional, yet uncharacterized anti-phage defense systems are encoded by bacteria and archaea genomes (Stern and Sorek, 2011).
A broad array of food products, commodity chemicals, and biotechnology products are manufactured industrially by large-scale bacterial fermentation of various substrates. Enormous amounts of bacteria are being cultivated each day in large fermentation vats, thus phage contamination can rapidly bring fermentations to a halt and cause economic setbacks, and is therefore considered a serious threat in these industries. The dairy fermentation industry has openly acknowledged the problem of phage and has been working with academia and starter culture companies to develop defense strategies and systems to curtail the propagation and evolution of phages for decades.
Anti-microbial phage therapy dates back to the early 1900s, after their co-discovery by Frederick Twort and Felix d'Hérelle (Twort F W 1915; and D'Hérelle 1917). Over the last decade a marked increase in interest in the therapeutic use of phages has been observed, which has resulted due to a substantial rise in the prevalence of antibiotic resistance of bacteria, coupled with an inadequate number of new antibiotics (Miedzybrodzki R et al., 2012). Properly formulated and applied phages have sufficient potential to cure bacterial infections. The key advantage of phages as anti-microbial therapeutic agents is their potential to negatively impact only their specific bacterial targets. Other advantages include, for example, an increase in phage number over the course of treatment, tendency to only minimally disrupt normal flora, capability of disrupting bacterial biofilms, low inherent toxicities, and most importantly effectiveness against both antibiotic-sensitive and antibiotic-resistant bacteria.
In 1982, Chinenova and colleagues reported a unique phage defense phenotype in Streptomyces coelicolor A3(2), which was denoted Phage Growth Limitation (PGL) (Chinenova T. A. et al, 1982). In their work Chinenova et al. demonstrated that upon the first cycle of infection by the ΦC31 phage, Streptomyces coelicolor A3 was phage-sensitive and supported phage burst. However, phages emerging from this first cycle of infection could not successfully re-infect the Streptomyces coelicolor A3 host. Intriguingly, these phages were able to successfully infect strains of Streptomyces that do not carry the PGL system (Chinenova T. A. et al, 1982).
Further studies mapped the phenotype to a cluster of four genes, denoted pglW, pglX, pglY and pglZ, which were shown to reconstitute the above described PGL phenotype upon transfer to a PGL host (Sumby. P. & Smith, M. C. 2002). Of note, introduction of pglY and pglZ− was not sufficient to confer a PGL+ phenotype in all mutants tested (Laity et al., 1993; Sumby et al. 2002). The domains encoded within these four genes do not resemble any classical combination of genes currently known to be involved in phage defense: pglZ is a member of the alkaline phosphatase superfamily; pglW has a serine/threonine kinase domain; pglX is an adenine-specific DNA methyltransferase; and pglY contains a p-loop ATPase domain (Sumby, P. & Smith, M. C. 2002). The PGL system described to date was not active against any other phage except for ΦC31 and its homoimmune relatives (Sumby. P. & Smith, M. C. 2002; Laity, C. et al. 1993).
A major characteristic of the PGL system described to date is the initial release of phage from the first infectious cycle followed by the attenuation of phage growth in the second. Various combinations of genes belonging to the PGL system, and predominantly pglZ, were found to be enriched within ‘defense islands’ (typical clustering of genes encoding defense system components in microbial genomes), providing additional support to the general involvement of these genes in a complex anti-phage defense system in multiple species (Makarova, K. S. et al. 2011; Makarova, K. S. et al. 2013). The discovery of the PGL system as an additional line of defense in bacteria may shed more light on the complex bacteria and phage arms race. However, a molecular mechanism that explains the activity of the PGL system has not yet been solved. Profound understanding of the molecular mechanism of this system might prove to be a powerful and economically important tool in molecular engineering applications (as was previously demonstrated with other complex phage resistance systems such as CRISPR-Cas).